Star Fruit (Carambola): Nutrients, What Research Shows and Safety

Star fruit, also called carambola, is the yellow-green, ribbed fruit of Averrhoa carambola L., a tropical tree in the wood sorrel family (Oxalidaceae). The whole fruit, skin included, is eaten fresh or juiced, and slices form a star shape. People eat it for its vitamin C and its fresh, tart taste. This page separates the fruit from extracts and leaf products, does not repeat hype, and puts one serious safety warning first: star fruit can poison people with kidney disease.

Read this first

• If you have kidney disease, are on dialysis, or have been told your kidneys are weak, do not eat star fruit or drink its juice. The National Kidney Foundation says people with kidney disease should avoid it because it contains a neurotoxin (a poison that affects the nervous system) that healthy kidneys can filter out but diseased kidneys cannot. [2] Reported signs are hiccups that will not stop, confusion, seizures and, in serious cases, death. [2]
• Case reports show that hospital patients on dialysis or with kidney failure have died after eating star fruit. [3][4] If someone with kidney disease has eaten star fruit and has hiccups, vomiting, confusion, numb limbs or a seizure, call 911 or your local emergency number and tell the team about the fruit.
• A few people with normal or unknown kidney function have also been harmed, in rare case reports, after drinking a lot of sour juice (one report advises against this especially on an empty stomach). Reported cases include sudden kidney injury from oxalate crystals. [7][8]
• Honest summary: by USDA figures star fruit is a good source of vitamin C. We found no human trial showing that eating it prevents or treats any disease. All other health claims come from lab or animal work. [15][16]

What is in it (USDA values)

Source: USDA FoodData Central, "Carambola, (starfruit), raw" (SR Legacy), item 171715. [1] % Daily Value uses the FDA 2016 Daily Values; values vary with variety, ripeness and storage. The USDA record we used has no oxalate figure. Reviews describe the fruit's oxalate content as high (see safety below). [15]

Lab analysis of star fruit has identified polyphenols (plant pigments with antioxidant activity in a test tube), including epicatechin, gallic acid forms and proanthocyanidins, plus vitamin C. [14] This is laboratory chemistry. We did not find a human trial showing that eating star fruit for these compounds improves health.

What research says

Eaten as food vs taken as a supplement or extract. The fruit is a source of vitamin C and fiber. The "medicinal" research is on leaf extracts, root compounds and juice in labs and animals. A result for one of these does not apply to a slice of fruit, and a nutrient in the fruit is not proof that it treats a disease. A 2021 review notes that clinical and safety research is limited compared with lab and animal work. [16]

How much is a normal serving

The USDA household portions are 1 cup of cubes (132 g), 1 cup sliced (108 g), or one medium fruit (91 g). [1] This is information, not a prescription. A review of poisoning reports says the amount of star fruit at which harm begins has not been established. [15] We did not read a source on dried or canned star fruit and give no figures for them. Whole fruit has fiber that juice lacks; see fruit juice vs whole fruit.

Safety, allergy and medicines

• Kidney disease: neurotoxicity. The National Kidney Foundation advises people with kidney disease to avoid star fruit. [2] In one series of 20 patients with kidney failure or on dialysis who became ill after eating star fruit or drinking its juice, eight died within five days despite emergency dialysis; survivors recovered with supportive care. [3] In 32 patients with kidney failure, the commonest symptoms were persistent hiccups, vomiting and disturbed consciousness. Those treated promptly with hemodialysis recovered without lasting problems, while severe cases left untreated or treated with peritoneal dialysis did not survive. [4] A Hong Kong series of seven patients reported hiccups, confusion, vomiting, impaired consciousness and high potassium, and its authors recommended that people with uremia (waste build-up from kidney failure) avoid star fruit entirely. [6] Seizures can become status epilepticus (seizures that do not stop). A review of published cases found seizures in 16 of 53 patients, with a reported 75% death rate in those patients. [5]
• The toxin. The suspected neurotoxin is caramboxin. A 2021 narrative review of 10 case series, 28 case reports (136 people) and 8 animal studies names oxalate and caramboxin as the causes of kidney and nerve harm; it says caramboxin blocks the calming brain messenger GABA from binding and activates glutamate receptors. [10] A fruit fraction caused seizures when put directly into rat brains. [11] The mechanism comes from animals and lab work, not from human trials.
• Kidney injury from oxalate (people who are not on dialysis). Two patients developed sudden kidney failure within hours of drinking large amounts of sour star fruit juice; biopsies showed oxalate crystals, and both recovered kidney function over about four weeks. [7] Two diabetic adults, one with normal kidney function before, developed oxalate-related kidney injury after a large amount of juice or many fruits and recovered within two weeks. [8] A 2026 case report describes sudden kidney injury after drinking large amounts of star fruit-infused liquor that later progressed to chronic kidney disease. [9] Risk factors listed in a review include chronic kidney disease, dehydration, eating on an empty stomach and the fruit's high oxalate content. [15] People with a history of kidney stones should ask a clinician; we did not find a source on star fruit and stone risk, so we say nothing more.
• Medicines. Lab tests on human liver tissue found star fruit juice strongly blocked the CYP3A enzyme that processes many medicines, more than grapefruit juice did in the same test. [12] Another lab test found it inhibited seven liver enzymes. [13] These are test-tube results; we did not find a study showing an effect on medicines in people. A pharmacist can check; see foods and medicine interactions.
• Allergy. We did not find a source we could read on star fruit allergy. For trouble breathing or swelling of the face or throat after any food, call 911. See when to seek medical help after a food reaction.
• Pregnancy. We did not find a readable official source on star fruit in pregnancy. Ask your midwife or doctor.
• Sugar. Star fruit has 3.98 g of sugars per 100 g. [1] People with diabetes can ask their care team how fruit fits their plan. Do not use star fruit leaf or root remedies for diabetes; the evidence is in animals.
• Supplements and leaf products. We did not find a human safety source for leaf or root extracts, so we make no claim about them.

Choosing, storing and food safety

• Wash produce under running water; do not use soap or produce wash, and scrub firm skins with a clean brush. [18]
• Cut away bruised or damaged areas, and refrigerate cut fruit at 40°F or below. [18]
• We did not find an official star fruit-specific storage or recall page we could read. Check current FDA and CDC recall notices if a product is recalled.

Related pages

• Foods, kidney disease, potassium and oxalates
• Foods and medicine interactions: vitamin K, grapefruit and others
• Fruit juice vs whole fruit
• Fresh, frozen and canned produce
• When to seek medical help after a food reaction
• Herbs and kidney disease